[filmscanners] RE: scanning at less than optical res

["LAURIE SOLOMON" <laurie@advancenet.net>]

>If you scan at 1200dpi, the scanner usually either samples all the 4800
>possible data points per inch and throws three out of every four away, or
>only samples every fourth possible point. So you are only getting one
>quarter of the possible data from the film. So why scan at large format if
>you are throwing three quarters of the film data away?

Bob, I beliee you are correct; but I do not understand your question. What
do you mean by "scan at large format" in this case?  I must have missed
something in the discussion.  The first method,which you note, involves the
actual sampling of original data using sampling algorithms and does result
in a loss of ortiginal data; but the second method, which you speak of with
respect to Vuescan and is available in almost all other scnning
applications, involves resampling of the original sample data using formulas
for combining and recombining data on the basis of all existing data and the
formulas.  Both methods, however, would involve the scanner reading during
the scan all 4800 points; so both would involve a "scan at large format" -
using your terms - or whatever optical format is used by the scanner.  After
the scan, everything else by way of sampling or resampling is either digital
conversion via hardware or software generated.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Bob Frost
Sent: Thursday, December 09, 2004 4:10 AM
To: laurie@advancenet.net
Subject: [filmscanners] scanning at less than optical res


Is this correct?


"As I understand things, a scanner with an
optical resolution of 4800dpi can take a sample reading every 1/4800 of an
inch. If you scan at the optical resolution, that is what is does and you
get 4800 readings per inch along that axis (usually a different resolution
on the other axis).

If you scan at 1200dpi, the scanner usually either samples all the 4800
possible data points per inch and throws three out of every four away, or
only samples every fourth possible point. So you are only getting one
quarter of the possible data from the film. So why scan at large format if
you are throwing three quarters of the film data away?

With Vuescan software, you can set it to scan all 4800 data points per inch,
but then to take the average of every four data points and reduce them to
one, so that the file you get out is the equivalent of a 1200dpi scan, but
all the data points have contributed to the final result."

Bob Frost.

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